Illumination optical system and image display apparatus making use thereof

ABSTRACT

An illumination optical system for illuminating a surface to be illuminated with a light beam from a light source, in a first plane which is parallel with the optical axis of the illumination optical system, the light beam from the light source is split, and a plurality of first light source images are formed in a first light source image zone with the use of the thus split light beams; light beams from the plurality of first light source images being led to the surface to be illuminated, in a second plane which is parallel with the optical axis of the illumination optical system and which is perpendicular to the first plane, the light beam from the light source is split, and a plurality of second light source images are formed in a second light source image zone, with the use of the thus split light beams, light beams from the plurality of second light source images being led to the surface to be illuminated, where the width of the first light source image zone in the first plane is greater than that of the second light source image zone in the second plane.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/249,943 filed Oct. 12, 2005, which claims priority to Japanese PatentApplication No. 2004-299788 filed Oct. 14, 2004, each of which is herebyincorporated by reference herein in its entirety. U.S. patentapplication Ser. No. 11/249,943 issued as U.S. Pat. No. 7,575,328 onAug. 18, 2009.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an illumination optical system forilluminating a surface to be illuminated, and further, relates to animage display apparatus (a liquid crystal projector or the like) inwhich a surface (an image display element such as a liquid crystalpanel) is illuminated with the use of the illumination optical system,and the light beam from the surface to be illuminated is projected ontoa projection surface such as a screen.

2. Description of the Related Art

Public attention has been focused on a projector having such aconfiguration that the light beam which has been modulated by a liquidcrystal light valve in accordance with image data, is enlarged andprojected onto a screen or the like. In this configuration of theprojector, it is important to display an image projected on the screenwith uniform brightness over the entire screen.

A well-known illumination optical system in the above-mentionedprojector, has a configuration as shown in, for example, FIG. 8. Thatis, a light beam emitted from a light source 101 is turned by aparabolic surface reflector 102 into a substantially parallel lightbeam, and is then output from the therefrom. This parallel light beam issplit and focused by a fly-eye lens (a lens array in which microspherical lenses are two-dimensionally arranged) 103. The respectivesplit light beams are focused in the vicinity of a second fly-eye lens104 so as to produce an image of the light source (a two-dimensionalimage of the light source). The micro lenses which constitute thesefly-eye lenses 103, 104 have a rectangular shape which is similar to theshape of the liquid display panel, that is, the surface to beilluminated. The split light beams output from the second fly-eye lensare focused by a condenser lens 105, and are led through a colorseparation optical system 106 and the like, and accordingly, theplurality of split beams illuminates the liquid crystal panel 107 insuperposition. It is noted that only essential components of theillumination optical system are shown in FIG. 8 in order to facilitatethe explanation of the function of the illumination optical system.

However, the above-mentioned illumination optical system, in general hasa tendency such that the higher the light available efficiency, thelarger the angular distribution of the light beam, and accordingly, hascaused a problem of deterioration of the image quality such asirregularity or lowering of contrast when an optical component which issensitive to an angular characteristic is used in the illuminationoptical system, and in particular, when a color separation film(dichroic mirror, dichroic prism or the like) or a polarizationseparation film (polarized film splitter or the like) inclined to theoptical axis of an illumination optical system is used in a colorseparation optical system.

In order to prevent the above-mentioned deterioration of the imagequality, there has been used an asymmetric optical system including anoptical element having a small angular distribution in a direction inwhich it is sensitive to the angular distribution but having a largeangular distribution in a direction in which it is insensitive to theangular distribution, as disclosed in Japanese Patent Laid-Open No.H06-75200 or Japanese Patent Laid-Open No. 2004-45907.

The Japanese Patent Laid-Open No. H06-75200 discloses a configurationwhich can reduce uneven color by using a cylindrical lens array which isa one-dimensional array serving as an optical integrator and as wellutilizing Koehler illumination in the bending direction of an elementwhich is highly sensitive to a one-dimensional angle, such as a dichroicmirror.

Further, Japanese Patent Laid-Open No. 2004-45907 discloses aconfiguration which can restrain the angular distribution of the lightbeam in one cross-sectional direction by setting a stop at a pupilposition in a direction in which an angular sensitivity of a thin filmcomponent is high, thereby it is possible to improve the contrast.

However, in the Japanese Patent Laid-Open No. H06-75200, no superposingillumination is made in a cross-section (Koehler illuminationcross-section) in which a cylindrical lens array has not a refractivepower, uniform illumination cannot be obtained at the light valvesurface. Accordingly, a relatively flat distribution should beselectively used from a nonuniform illumination distribution, resultingin low light available efficiency. Further, since the light beam fromthe light source to the condenser lens has a small angular distribution,although an image quality deteriorating effect by the dichroic mirrorlocated therebetween is reduced, image quality deterioration caused byan element having a high angular sensitivity, such as a liquid crystalpanel or the dichroic mirror, located after the condenser lens isinevitable as the light beam is converged by the condenser lens justbefore the liquid crystal panel. Further, in the cross-section in whichno superposing illumination is made, when the light source causes unevenbrightness due to fluctuation (arc jump, deterioration or the like) ofthe light source, the illumination distribution of the light valve alsovaries, resulting in unevenness at a projected screen.

Further, in the Japanese Patent Laid-Open No. 2004-45907, superposingillumination is made in cross-sections in both direction, although thelight source can hardly have an effect, extreme lowering of the lightavailable efficiency is inevitable since the light beam is limited by astop. There has been disclosed such a configuration that the principlepoint positions of a part of lenses (an optical system between the lensarray and the panel), other than the stop, are different from each otherbetween two cross-sections in order to cause angular distributions inthe two cross-sections to be different from each other. However, in amethod stated in the description of the embodiments (a principal pointof a collimator lens is changed), the boundary of the illumination zoneat the surface of the liquid crystal display panel is unclear, resultingin lowering of brightness or uneven illumination. Further, since thetelecentric condition (the exit pupil is sufficiently far from the panelsurface) becomes unsatisfactory, there has been raised such a problemthat uneven contrast and uneven color would be caused.

SUMMARY OF THE INVENTION

The present invention is devised in view of problems as mentioned above,and accordingly an object of the present invention is to provide anillumination optical system which can reduce the angular distribution ina section where an arbitrary optical component has a sensitive angulardistribution, and in which brightness is uniform on the light valve soas to substantially avoid effects caused by unevenness of the lightsource.

According to a first aspect of the present invention, there is providedan illumination optical system for illuminating a surface to beilluminated with a light beam from a light source, wherein the lightbeam from the light source is split in a first plane which is parallelto the optical axis of the illumination optical system, a plurality offirst source images are formed in a first light source image zone withthe use of the thus split light beams, and light beams from theplurality of first light source images are led to the surface to beilluminated,

the light beam from the light source is split in a second plane which isparallel to the optical axis of the illumination optical system andwhich is perpendicular to the first plane, a plurality of second sourceimages are formed in a second light source image zone with the use ofthe thus split light beams, and light beams from the plurality of secondlight source images are led to the surface to be illuminated, and

the width of the first light source image zone in the first plane islarger than that of the second light source image zone in the secondplane.

Further, according to a second aspect of the present invention, there isprovided an illumination optical system for illuminating a surface to beilluminated with light from a light source through the intermediary of apolarization separation surface, in which a second plane which isparallel with a normal line to the polarization separation surface andthe optical axis of the illumination optical system, and a first planewhich is perpendicular to the second plane and which is parallel withthe optical axis of the illumination optical system are defined,comprising: being arranged successively in the mentioned order from thelight source,

a first front side cylindrical lens array including a plurality ofcylindrical lenses having refractive powers in the first plane,

a first rear side cylindrical lens array including a plurality ofcylindrical lenses having refractive powers in the first plane,

a second front side cylindrical lens array including a plurality ofcylindrical lenses having refractive powers in the second plane, and

a second rear side cylindrical lens array including a plurality ofcylindrical lenses having refractive power in the second plane.

Further, according to a third aspect of the present invention forilluminating a surface to be illuminated with light from a light sourcethrough the intermediary of a polarization separation surface, in whicha second plane which is parallel with a normal line to the polarizationseparation surface and the optical axis of the illumination opticalsystem, and a first plane which is perpendicular to the second plane andwhich is parallel with the optical axis of the illumination opticalsystem are defined, there is provided an illumination optical systemcomprising:

a plurality of lenses having refractive powers in a first plane,arranged in the direction of the first plane, and

a plurality of lenses having refractive powers in the direction of thesecond plane, and arranged in the direction of the second plane,

wherein the number of lenses of the plurality of lenses arranged in thefirst plane is larger than in the second plane.

According to fourth aspect of the present invention there is provided anillumination optical system comprising:

a first optical element array including a plurality of optical elementshaving refractive powers in a first plane containing the optical axis,for splitting light from an optical source into a plurality of partiallight beams,

a second optical element array including a plurality of optical elementshaving refractive powers in the first plane, for transmitting theplurality of partial light beams onto a surface to be illuminated,

a superposing optical element for superposing the plurality of partiallight beams output from the second optical element array with oneanother on the surface to be illuminated,

the arrangement of refractive powers in the first plane being differentfrom that in the second plane which contains the optical axis and whichis perpendicular to the first plane, and

a compressing device for compressing the width, in the first plane, ofthe light beam from the light source.

Further, according to a fifth aspect of the present invention, there isprovided an image display apparatus comprising:

at least one liquid crystal display element, and an illumination opticalsystem according to the first aspect of the present invention, forilluminating the at least one liquid crystal display element with lightfrom the optical source.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a sectional view illustrating an illumination optical systemin a first embodiment of the present invention, in a first plane,

FIG. 1B is a sectional view illustrating the illumination optical systemshown in FIG. 1A in a second plane;

FIG. 2 is a perspective view illustrating a cylindrical lens array inthe first embodiment of the present invention,

FIG. 3A is a sectional view illustrating the light source imageformation zone in the first embodiment of the present invention, in thefirst plane,

FIG. 3B is a second sectional view illustrating the light source imageformation zone shown in FIG. 3A, in the second plane,

FIG. 4A is a sectional view illustrating an illumination optical systemin a second embodiment of the present invention,

FIG. 4B is a sectional view illustrating the illumination optical systemshown in FIG. 4A, in a second plane;

FIG. 5 is a view illustrating an image display apparatus (projector) inaccordance with a third embodiment of the present invention,

FIG. 6A is a sectional view illustrating an illumination optical systemin a variant of the third embodiment of the present invention, in afirst plane,

FIG. 6B is a sectional view illustrating the illumination optical systemshown in FIG. 6A, in a second plane,

FIG. 7 is an image view illustrating an optical image according to thesecond embodiment of the present invention,

FIG. 8 is a sectional view illustrating the configuration of aconventional projector, and

FIG. 9A is a view for explaining parameters W1′, W2′ in a first plane,and

FIG. 9B is a view for explaining parameters W1′, W2′ in a second plane.

DESCRIPTION OF THE EMBODIMENTS

Explanation will be made of embodiments of the present invention withreference to the accompanying drawings.

First Embodiment

Referring to FIGS. 1A and 1B which show the configuration of anillumination optical system in an embodiment of the present invention,the illumination optical system in the embodiment is used as anillumination optical system in a projector using a reflection typeliquid crystal panel as an image display element (a transmission typeliquid crystal pane can also be used).

It is noted here that the illumination optical system has the opticalaxis in the Z-axial direction. FIGS. 1A and 1B show a section in whichthe light beam incident upon a panel surface has a wide angulardistribution (a first section or an YZ plane), and FIG. 1B shows asection in which the light beam has a narrow angular distribution (asecond section or an XZ plane). Although these figures show onlyfundamental components of the projector optical system in order tosimplify the explanation thereof, there can be of course used aconfiguration having a polarization converting element array in whichpolarization converting elements for converting unpolarized light intolinearly polarized light are arrayed, a mirror for bending the opticalpath, an infrared cut-off filter, a polarizing plate and the like.

A light beam emitted from a light source (a light emitting part of alamp) 1 omnidirectionally is turned by a parabolic reflector 2 into asubstantially parallel light beam which is then output. This light beamis split by a first cylindrical lens array (which corresponds to anoptical element array and which is shown in FIG. 2 in a perspectiveview) 3 into a plurality of partial light beams which are thenconverged. These split light beams are converged in the vicinity of asecond cylindrical lens array 4 so as to form light source images(secondary light source images), respectively. In this embodiment, thelight source images obtained by the action of the first cylindrical lensarray as mentioned above are shown in FIG. 3A which shows the locationof the light source images in a plane perpendicular to the optical axisand in which the first section can be shown as a straight line. In thiscase, W1 is the width of the zone where the light source images areformed, in the first section (inward direction). The width W1 of thelight source image forming zone at positions where the light sourceimages are formed, (the positions of the second cylindrical lenseshaving refractive powers in the first section in this embodiment orincident positions) is set to be maximum (or is the width obtained bycutting the zone by a section containing the optical axis) among widthsof light source image zones which are obtained by cutting the lightsource image forming zone by various sections which are parallel withthe first section. Incidentally, it is desirable as to the boundary forW1 to select the distance between two positions which are locatedendmost among positions where the brightness is ½ (which can changed to1/10) of brightness of a point which is maximum within the light sourceimage forming zone (It is of course possible to select the distancebetween two positions which are located endmost in the light sourceimage forming zone or the distance between the brightness center of aband-like light source image located at one endmost side and thebrightness center of a band-like light source image located the otherendmost side). This matter is similar to W2 which will be describedlater.

Since these cylindrical lens arrays 3, 4 have refractive powers only inthe first section, and accordingly, they do not substantially affect thelight beam in the second section which is perpendicular to the firstsection. Meanwhile, an afocal optical system (a light beam compressingdevice which is in this case an optical system for emerging a parallellight beam while narrowing the diameter thereof) 5, a third cylindricallens array 6, a fourth cylindrical lens array 7 and a cylindrical lensarray 9 have no refractive powers in the first section. Accordingly, thesplit light beams output from the second cylindrical lens array 4 areconverged by the condenser lens 8 without being affected in the firstsection by the above-mentioned optical elements which have refractivepowers (optical powers) in only the second section, and then illuminatethe reflection type liquid crystal panel 11 in a superposing manner byway of a color separation optical system 10 which is configured to havea polarized beam splitter positioned at an inclination to the opticalaxis of the illumination optical system (at an inclination so that theoptical axes of the illumination optical system and the polarized beamsplitter make therebetween an angle of 45 deg. or in a range from 42 to48 deg.). it is of course also possible to use another configurationhaving a dichroic mirror or a dichroic prism. It is noted that thepolarized beam splitter as stated above is an optical element which hasa polarization separation characteristic (such a characteristic thatlight in one of polarizing directions is reflected by not less than 80%of light which is incident thereupon at a predetermined angle, but lightin the other direction orthogonal to the one direction is transmitted bynot less than 80%) for light at least in a part of the visible lightregion (which, in at least one exemplary embodiment, is at least notgreater than 10 nm), and is not always necessary to be an opticalelement having a polarization separation characteristic for light in theentire visible light region.

Next, explanation will be made of the behavior (variation) of an opticalbeam in the second section. In the second section, the light beam whichis output as substantially parallel light from the reflector 2 comes tothe afocal optical system 5 without being affected by the first andsecond cylindrical lens arrays 3, 4. The afocal optical system 5compresses the incident parallel light beam and outputs the light beamhaving a decreased beam diameter in the second section as again aparallel light beam. Although the afocal optical system 5 which iscomposed of a convex lens and a concave lens in combination is shown inFIG. 1B, it can be composed of convex lenses in combination wheneverthey can constitute a focal optical system. It is of course possible tohave other than two lenses. Further, it can be considered that theafocal optical system can be composed of elements other than lenses. Forexample, the afocal optical system can be composed of an ellipticreflector and a concave (convex) lens in combination in such a case thatthe reflector 2 serves as a parabolic reflector (which outputs lightfrom the light source as substantially parallel light) in the firstsection, but it serves as a so-called sculptured surface (rotationallyasymmetrical surface) having the shape of an elliptic reflector (whichoutputs light from the light source as a converged light beam). Further,even though the reflector 2 has the shape of an ordinary ellipticreflector, if positions at which the converged light output therefrom isconverted into parallel light are different from each other between thefirst section and the second section, the beam diameter in the firstsection and the beam diameter in the second section can be differentfrom each other.

The parallel light beam output from the afocal optical system 5 and thenconverged is split by the third cylindrical lens array 6 into splitlight beams which are then focused in the vicinity of the fourthcylindrical lens array 7 so as to form the light source images. FIG. 3Bshows the light source images which are formed by the third cylindricallenses having refractive powers in the direction of the second section,in this embodiment. FIG. 3B shows the light source images in a planeperpendicular to the optical axis of the illumination optical system,and an example of the second section in FIG. 3B can be depicted by astraight line as in the second section (one example) shown in FIG. 3B.In this case, the width in the direction of this section is set to W2.

As understood by the comparison between FIGS. 3A and 3B, the width W2 ofthe light source image in the second section is narrower than the widthW1 of the light source image in the first direction. The sizerelationship (ratio) between W1 and W2 can directly correspond to a sizerelationship (ratio) between angular distributions at the polarized beamsplitter, and accordingly, the relationship therebetween is desirablyset to W1>W2, that is, W2/W1, in at least one exemplary embodiment, canbe less than 0.8 but greater than 0.1. and in yet another embodiment canbe less than 0.6 but greater than 0.3. In view of the above-mentionedconditional formula, should the upper limit be exceeded, such an effectthat the contrast is heightened may not be sufficiently obtained, anduneven brightness would be exhibited on the surface to be illuminatedsuch as a liquid crystal display element without being satisfactorilyimproved. Moreover, should the lower limit be not exceeded to such anextent that the light beam split and converged by an arbitrary lens inthe third cylindrical lens array 6 is not incident upon thecorresponding cylindrical lens cell but is incident upon a differentlens cell in the fourth cylindrical lens array 7 would be increased. Thelight beams which are not incident upon the corresponding lens cellscome in part to positions out of an effective zone on the surface to beilluminated, and accordingly, they become ineffective. That is, thelight available efficiency would be lowered. In the case of notexceeding the lower limit as stated above, the percentage of light whichdoes not come to the surface to be illuminated is abruptly increased,and accordingly, the brightness obtained in a projector is greatlydecreased. It is noted that W1 and W2 can be taken respectively as thebeam diameter of the light beam which is incident upon the secondcylindrical lens array, in the first section, and as the beam diameterof the light beam incident upon the fourth cylindrical lens array, inthe second section. Further, as shown in FIGS. 9A and 9B, in such a casethat the distance between the optical axis of a cylindrical lens at oneend side of the second cylindrical lens array and the optical axis of acylindrical lens at the other end side is set to W1′ while the distancebetween the optical axis of a cylindrical lens at one end side of thefourth cylindrical lend array and the optical axis of a cylindrical lensat the other end side is set to W2′, the relationship therebetween isdesirably set to W1′>W2′, that is, W2′/W1′, in at least one exemplaryembodiment, can be less than 0.8 but greater than 0.1. and in yetanother embodiment can be less than 0.6 but greater than 0.3.

The split light beams output from the fourth cylindrical lens array 7are converged by the condenser lens 8 and the cylindrical lens array 9and illuminate the reflection type liquid crystal panel 11 in asuperposing manner by way of the color separation optical system 10having the polarized beam splitter and the like. The condenser lens 8 isa spherical lens having equal refractive powers in both first and secondsections (It is of course possible to use two lenses one of which has arefractive power only in the first section and the other one of whichhas a refractive power only in the second section, instead of thecondenser lens 8).

Referring to FIGS. 1A and 1B, it is required that the refractive powersfor converging the split light beams are greater in the second sectionwhere the cylindrical lens array is located at a position nearer to thepanel side than in the first section, and accordingly, refractive powersfor the condensing lenses are increased by the cylindrical lens array10. Cylindrical lenses can of course be added in the respectivesections. Further, toroidal lenses having different refractive powersbetween the first and second surfaces can be used so as to exhibitsimilar effects. Further, although the fourth cylindrical lens array 8has at its rear surface a negative refractive power which is required insuch a case that the third and fourth cylindrical lens arrays 7, 8 haveone and the same pitches, a similar function can be materialized bymaking cylindrical lenses in a cylindrical lens array to be eccentric ormaking the pitches of the cylindrical lens array to be different betweenthe third cylindrical lens array and the fourth cylindrical lens arrays.

In this embodiment, although the beam diameter of the light beam outputfrom the reflector is compressed not in the first section but in thesecond section so as to make the width of the light source image formingzone in the first section different from that in the second section, thepresent invention is not limited to this configuration. For example, thebeam diameter can be compressed in both first and second sections, andas well the beam diameter can be compressed in one section but beenlarged in the other section while the beam diameter can be enlarged inboth sections. An optical system having functions of compressing andenlarging the light beam in both first and second sections can not beused if the shape of the reflector is appropriate (the beam diameter ofthe light beam output from the reflector is different between the firstsection and the second section). If the width of the light source imageforming zone is different between the first section and the secondsection, and if the width W2 of the light source image forming zone in asection which is sensitive to the angular distribution (a section whichis parallel with both normal line to the polarization separation surfaceof the polarized beam splitter and optical axis of the illuminationoptical system, that is, the second section in this embodiment) and thewidth W1 of the light source image forming zone in a section which isperpendicular to the former section and which is insensitive to theangular distribution (that is, which is parallel with the optical axisof the illumination optical system) satisfy the above-mentionedcondition, any configuration can be used.

With the configuration as stated above, as shown in FIGS. 1A and 1B, theangular distribution of the illumination light beam incident upon thereflection type liquid crystal panel (the surface to be illuminated) 11in the second section is narrowed with respect to the first section(after passing through a final optical element having a refractive powerin the illumination optical system). The polarized beam splitter locatedin the color separation optical system 10 which is arranged in front ofthe reflection type liquid crystal panel 11 is adapted to bend a part ofthe optical paths of the light beams in the second section. Ageneral-purpose dielectric multi-film polarized light splitter carriesout polarization separation with the use of the difference betweenP-polarization and S-polarization at a Brewster angle, the further thedeviation of the light beam from the Brewster angle, the moreinsufficient the polarization separation. Accordingly, should anillumination optical system having a wide angular distribution be used,polarized light to be transmitted would be reflected or polarized lightto be reflected would be transmitted. Thus, light (leakage light) havinga polarized state different from a desired polarized light would beincident upon the liquid crystal panel, resulting in lowering of thecontrast. However, in the illumination optical system in thisembodiment, since the angular distribution in a section which issensitive to the angular distribution is set to be smaller than theangular distribution in a section which is insensitive to the angulardistribution, the degree of generation of leakage light in a sectionwhich is sensitive to the angular distribution can be restrained,thereby it is possible to obtain an image having a high contrast.

Further, W1 and W2 as stated above can be substituted as follows so asto satisfy the above-mentioned conditional formula. In an illuminationoptical system comprising a first cylindrical lens array (a first frontside optical element array) 3 for splitting a light beam from a lightsource into a plurality of partial light beams in a first section andfor converging the respective partial light beams, a second cylindricallens array (a first rear side optical element array) 4 located in thevicinity of converged positions of the plurality of the partial lightbeams and having a plurality of optical elements corresponding to theplurality of partial light beams, for leading the partial light beams tothe surface to be illuminated such as a reflection type liquid displaypanel, a third cylindrical lens array (a second front side opticalelement array) 6 for splitting a light beam from the light source into aplurality of partial light beams in a second section and for convergingthe plurality of partial light beams, and a fourth cylindrical lensarray (a second rear side optical element array) 7 located in thevicinity of converged positions of the plurality of the partial lightbeams and having a plurality of optical elements corresponding to theplurality of partial light beams, for leading the partial light beamsonto the surface to be illuminated such as the reflection type liquidcrystal panel, the width of the second optical element array (the firstrear side optical element array) 4 in the first section (the distancefrom one end to the other end of cylindrical lenses belonging to thesecond cylindrical lens array, or the distance from the top position orthe top surface of a cylindrical lens arranged nearest to one end sideof the plurality of cylindrical lenses to the top position or the topsurface of a cylindrical lens arranged nearest to the other end side)can be set to W1 while the width of the fourth cylindrical lens array(the second rear side optical element array) 7 in the second section(the distance from one end to the other end of the plurality ofcylindrical lenses belonging to the fourth cylindrical lens array, orthe distance from the top position or the top surface of a cylindricallens arranged nearest to one end side of the plurality of cylindricallenses to the top position or the top surface of a cylindrical lensarranged nearest to the other end side) can be set to W2, and then, aconditional formula as stated above can be set.

Further, the number of cylindrical lenses of the first and secondcylindrical lens arrays arranged in the first section is larger thanthat of the third and forth cylindrical lens arrays in the secondsection. In at least one exemplary embodiment, the number of cylindricallenses of the first and second cylindrical lens arrays is not less than1.3 times (in yet another embodiment, not less than 1.6 times) but notgreater than 3 times (in yet another embodiment 2.5 times or more, andin another embodiment 2 times) as large as large as that of the thirdand fourth cylindrical lens arrays.

Further, in the second section, since the beam diameter of the beambefore being incident upon the panel is narrow (the angular distributionis narrow or the enlarging angle of each of the beams is small), thepolarized beam splitter itself can be small-sized, thereby it ispossible to contribute to miniaturization of the illumination opticalsystem.

In this embodiment, although the afocal system 5 has a refractive powerin the second section, the third and fourth cylindrical lens arrays 6,7, the condenser lens 8 and the cylindrical lens array 9 are arranged onthe rear side of the second cylindrical lens array (on the liquidcrystal display side) 4, the present invention is not limited to thisconfiguration. That is, the afocal system 5, the third and fourthcylindrical lens array, the cylindrical lens array 9 and the like (apart or all thereof) can be arranged on the front side of the secondcylindrical lens array 4 (the first cylindrical lens array 3) (on thelight source side). Specifically, if the first and second sections areindependent from each other in view of their refractive powers so thatno problem of physical interference is caused, they can be arranged inany configuration.

Further, there would be such a case that the polarization convertingelement (polarized beam splitter array) is arranged in the vicinity ofthe lens array in order to enhance the light available efficiency.Although it is not shown, it is desirable to arrange the polarizationconverting element on the rear side of the second cylindrical array 4 oron the rear side of the fourth cylindrical lens array 7. In particular,in the case of the arrangement on the rear side of the array 7, theelement can be small-sized in comparison with a conventional one, andaccordingly, there might be obtained such merits that the apparatus canbe miniaturized and simplified, and the costs of the apparatus can bereduced as a whole.

With the configuration of this embodiment as stated above, anillumination optical system having two sections having different angulardistributions can be materialized, and accordingly, even an opticalsystem using an optical element which is sensitive to an angularcharacteristic can restrain deterioration of its performance. Inparticular, in a projector, it is possible to produce an image having ahigh contrast.

Second Embodiment

Referring to FIG. 4 which shows a second embodiment of the presentinvention, in this embodiment, the lens arrays are commonly used in bothfirst and second sections. The lens arrays 13, 14 in this embodiment areso-called fly-eye lens arrays in which spherical lenses aretwo-dimensionally arranged.

In the second section, an afocal system composed of concave and convexcylindrical lenses in combination carries out compression of an opticalbeam on the light source side of the lens arrays 13, 14. With thisconfiguration, the lens arrays 13, 14 in this embodiment have sideshaving different lengths (the width of the incident light beam in thedirection of the first section and the width thereof in the direction ofthe second section) between the first section and the second section,and the width in the first section (the length of the side in thedirection of the first section) is greater than the width in the secondsection (the length of the side in the direction of the second section).The light beams split and converged by the lens array 13 constitute agroup of light source images in the vicinity of the lens array 14. FIG.7 shows an image of the group of light source images (an image in aplane perpendicular to the optical axis). The number of light sourceimages is not, of course, limited to that shown in FIG. 7, but it issufficient if any plural number of light source images are formed twodimensionally. It is noted here that the relationship between W1 and W2as stated in the first embodiment is satisfied even as to the lightsource image forming zone in which these light source images are formed.Incidentally, the width W1 of the light source image forming zone in thefirst section is the maximum one of widths of the light source imageforming zone which are obtained by cutting the light source imageforming zone in which a plurality of light source images are formed (inat least one exemplary embodiment it can be the maximum one of distancesfrom one endmost side part of the light source image at one endmost sideamong the plurality of light source images to the other endmost sidepart of the light source image at the other endmost side, distance fromthe gravitational center of brightness of the light source image at oneendmost side to the gravitational center of brightness of the lightsource image at the other endmost side, or half-width values that is,distances between positions at which the brightness becomes half of themaximum brightness of the light source image at one end most side and aposition at which the brightness becomes half to the maximum brightnessof the light source image at the other endmost side), by a plurality ofplanes which are parallel with the first section (that is, in sectionsin parallel with the first section), and the width W2 in the secondsection is a distance similar to that as stated above. Thus, even in thesecond embodiment, W1 and W2 can be different from each other(asymmetric), and accordingly, technical effects similar to those in thefirst embodiment can be obtained. The configuration of the secondembodiment is similar to that of the first embodiment, except thatfly-eye lenses are used in order to commonly used optical membersbetween the first (second) cylindrical lens array having refractivepowers in the first section and the third (fourth) cylindrical arrayhaving refractive powers in the second section. With this configuration,the number of components can be reduced, thereby it is possible toobtain such technical effects that the configuration of the illuminationoptical system can be simplified, the yield can be enhanced and thecosts can be reduced.

However, since the lens cells of the lens array 13 and the surface to beilluminated have a conjugate relationship therebetween, it is requiredthat the shape of the lens cells follows the aspect ratio of the liquidcrystal panel. Thus, in the case of the compression of the light beam inthe second section, the shape of the lens cells cannot be itselfnarrowed, and accordingly, it is required to reduce the number of thelens cells in the second section. If the number of the lens cells isdecreased, the effect of improvement in unevenness over the surface tobe illuminated possibly becomes lower, resulting in limitation to thecompression of the light beam, and therefore, the degree of freedom ofdesign becomes less in comparison with that of the first embodiment.Thus, it is desirable that the configuration of the second embodimentsatisfies the conditional formula as to W1 and W2. Further, it isdesirable to arrange at least not less than three of lens cells havingrefractive powers in the second section, in the direction of the secondsection, and further, it is desirable to set the number of lens cellshaving refractive powers in the first section to a value which is notless than 1.3 times (in yet another embodiment not less than 1.6 times)but not greater than 3 times (or in yet another embodiment 2.5 times) aslarge as that of the lens cells having refractive powers in thedirection of the second section.

As a variant of this embodiment, the compression of the light beam canbe made between the lens arrays 13, 14. Specifically, as shown in FIG.6, there are provided a first optical element 23 formed on its onesurface (the surface on the light source side) with a fly-eye lenssurface and on its the other surface (the surface on the surface side tobe illuminated) with a convex lens surface, and a second optical element24 formed on its one surface (the surface on the light source side) witha concave lens surface and on its the other surface (the surface on thesurface side to be illuminated) with a fly-eye lens surface. With thisconfiguration, the number of components can be further decreased,thereby it is possible to provide a projectors having lower costs. Inthis configuration, the order of arrangement of the first opticalelement and the second optical element can be reversed. Further, theconfiguration of the afocal system is not limited to the combination ofa convex lens surface and a concave lens surface, but the combination ofa convex surface and a convex lens surface, of an elliptic reflectionsurface and a concave lens surface and so forth can also be used.

Third Embodiment

Referring to FIG. 5 which is a view illustrating an image displayapparatus (projector) composed of an illumination optical system 100 asstated in the above-mentioned first and second embodiments, there areshown a the light emitting bulb 41 for emitting white light withcontinuous spectrum, and a reflector 42 for converging light from thelight emitting bulb 41 in a predetermined direction, both light emittingbulb 41 and the reflector 42 constituting a lamp 40. The light from thelamp 40 is led to a liquid crystal display element (a reflection typeliquid crystal panel or the like) with the use of the illuminationoptical system 100 as stated in the above-mentioned first and secondembodiments 1. Detailed description will be hereinbelow made.

Also referring to FIG. 5, there are shown a dichroic mirror 58 forreflecting light in wavelength ranges of blue (B) and red (R) buttransmitting therethrough light in a wavelength range of green (G), theincident side polarizing plate 59 for G light, formed of a polarizerapplied over a transparent substrate, which transmits only S-polarizedlight therethrough, and a first polarized beam splitter 60 having apolarization separation film, for transmitting therethrough P-polarizedelement but reflecting S-polarized light.

Further, there are shown a red light reflection type liquid crystaldisplay element 61R, a blue light reflection type liquid crystal displayelement 61B and a green light reflection type liquid crystal displayelement 61G, for reflecting incident light and performing imagemodulation, a ¼ wavelength plate 62R for red light, a ¼ wavelength plate62G for green light, a ¼ wavelength plate 62B for blue light, anincident side polarizing plate 64 for RB light, formed of a polarizerapplied over a transparent substrate, which transmits therethrough onlyS-polarized light, a first color selective phase difference plate 65which changes the polarizing direction of B light by an angle of 90deg., but does not change the polarizing direction of R light, a secondpolarized beam splitter 66 having a polarization separation film, fortransmitting therethrough P-polarized light but reflecting S-polarizedlight, and a second color selective phase difference plate 67 whichchanges the polarizing direction of R light by an angle of 90 deg., butdoes not change the polarizing direction of B light.

Further, there are shown an emergent side polarizing plate (polarizer)68, for transmitting only S-polarized light, and a third polarized beamsplitter 69 (color synthesizing device) having a polarization separationfilm, for transmitting therethough P-polarized light but reflectingS-polarized light. A color separation and synthesis optical system 200is constituted by the components ranging from the dichroic mirror 58 tothe third polarized beam splitter 69.

There is shown a projection lens optical system 70. The above-mentionedillumination optical system, the color separation and synthesis opticalsystem and the projection lens optical system constitute an imagedisplay optical system.

Next, explanation will be made of optical action after light passesthrough the illumination optical system. At first, the G optical pathwill be explained.

G light which has passed through the dichroic mirror 58 is incident uponthe incident side polarizing plate 59. The G light is still S-polarizedlight after the light is separated by the dichroic mirror 58. Further,after emerging from the incident side polarizing plate 59, the G lightis incident as S-polarized light upon the first polarized beam splitter60 and is reflected at the polarization separation film, and then comesto the G light reflection type liquid crystal display element 61G. Inthe G-light reflection type liquid crystal display element 91G, G-lightis image-modulated and reflected. An S-polarized component of reflectedlight of the image-modulated G-light is again reflected at thepolarization separation film of the first polarized beam splitter 60 andis returned to the light source side so as to be removed from theprojection light. Meanwhile, a p-polarized component of the reflectionlight of the image-modulated G-light is transmitted through thepolarization separation film of the first polarized beam splitter 60,and is directed as projection light to the third polarized beam splitter69. At this time, in a condition in which all polarized components arechanged into S-polarization (a condition in which black is displayed),the phase lag axis of the ¼ wavelength plate 62G arranged between thefirst polarized beam splitter 60 and the G-light reflection type liquidcrystal display element 61G is adjusted to a predetermined direction sothat affection by disturbance in a polarized condition, which occurs atthe first polarized beam splitter 60 and the G-light reflection typeliquid display element 61G can be held to a small value. G-light outputfrom the first beam splitter 60 is incident upon the third polarizedbeam splitter 69 in a P-polarized state, then transmits through thepolarization separation film in the third polarized beam splitter 69,and comes to the projection lens 70.

Meanwhile, R- and B-light reflected by the dichroic mirror 58 isincident upon the incident side polarizing plate 64. It is noted thatthe R- and B-light is still S-polarized even after they are separatedfrom each other by the dichroic mirror 58. Further, the R- and B-lightis output from the incident side polarizing plate 64, and is thereafterincident upon the first color selective phase difference plate 65. Thefirst color selective phase difference plate 65 has such a function thatonly the polarizing direction of the B-light is rotated by an angle of90 deg., and accordingly, the B-light which is P-polarized and theR-light which is S-polarized are incident upon the second polarized beamsplitter 66. The R-light which is S-polarized and incident upon thesecond polarized beam splitter 66 is reflected by the polarizationseparation surface of the second polarized beam splitter 66, and thencomes to the R-right reflection type liquid crystal display element 61R.Further, the B-right which is P-polarized and incident upon the secondpolarized beam splitter 66 is transmitted through the polarizationseparation surface of the second polarized beam splitter 66, and thencomes to the B-light reflection type liquid crystal display element 61B.

The R-light incident upon the R-light reflection type liquid crystaldisplay element 61R is image-modulated and reflected. The S-polarizedcomponent of the image-modulated and reflected R-light is transmittedagain through the polarization separation surface of the secondpolarized beam splitter 66, and is then returned to the light sourceside so as to be removed from the projection light. Meanwhile, theP-polarized component of the image-modulated and reflected R-light istransmitted through the polarization separation surface of the secondpolarized beam splitter 66, and then is directed, as projection light,to the second color selective phase plate 67.

Further, the B-light incident upon the B-light reflection type liquidcrystal display element 61B is image-modulated and reflected. TheP-polarized component of the image-modulated and reflected B-light isagain transmitted through the polarization separation surface of thesecond polarized beam splitter 66, and is then returned to the lightsource side so as to be removed from the projection light. Meanwhile,the S-polarized component of the image-modulated and reflected B-lightis reflected by the polarization separation surface of the secondpolarized beam splitter 66, and is directed, as projection light, to thesecond color selective phase plate 67.

At this time, by adjusting the phase lag axes of the ¼ wavelength plates62A, 62B provided between the second polarized beam splitter 66 and theR- and B-right reflection type liquid crystal display elements 62R, 62B,black display adjustment respective for the R- and B-light can becarried out, similar to the G-light.

Thus, the lights are synthesized into a single light beam, of theR-projection light and the B-projection light output from the secondpolarized beam splitter 66, the R-light is turned into an S-polarizedcomponent with its polarizing direction being rotated by an angle of 90deg., by the second color selective phase plate 67, and is analyzed bythe emergent side polarizing plate 68 before it is incident upon thethird polarized beam splitter 69. Further, the B-light which is still inthe S-polarized state as it is, is transmitted through the second colorselective phase plate 67, and is then analyzed by the emergent sidepolarizing plate 68 before it is incident upon the third polarized beamsplitter 69. It is noted that the R-projection light and B-projectionlight are analyzed by the emergent side polarizing plate 68 so as to betuned into light from which ineffective components caused by passing thesecond polarized beam splitter 66 and the R- and B-light reflection typeliquid crystal display elements 61R, 61B and the ¼ wavelength plates62R, 62B are cut off.

Further, the R-projection light and the B-light which are incident uponthe third polarized beam splitter 69 are reflected at the polarizationseparation surface of the third beam splitter 69, then is synthesizedwith G-light reflected from the above-mentioned polarization separationsurface, and thereafter come to the projection lens 70.

Then, the synthesized R, G, B projection light is enlarged and projectedonto the surface to be illuminated such as a screen, by the projectionlens 70.

The optical path as stated above concerns such a case that thereflection type liquid crystal display elements exhibit white, andaccordingly, explanation will be hereinbelow made of the optical path insuch a case that the reflection type liquid crystal display elementsexhibit black.

At first, explanation will be made of the G-light path.

The S-polarized component of G-light which has been transmitted throughthe dichroic mirror 58 is incident upon the incident side polarizingplate 59, then is incident upon the first polarized beam splitter 60 soas to be reflected by the polarization separation surface, and comes tothe G-light reflection type liquid crystal display element 61G. However,since the reflection type liquid crystal display element 61G exhibitsblack, the G-light is reflected without being image-modulated. Thus,even after the reflection upon the reflection type liquid crystaldisplay element 61G, the G-light is still S-polarized as it is, andaccordingly, is again reflected by the polarization separation surfaceof the first polarized beam splitter 60. It is then transmitted throughthe incident side polarizing plate 59, and is returned to the lightsource side so as to be removed from the projection light.

Next, explanation will be made of optical paths for the R- and B-light.

S-polarized components of the R- and B-light reflected from the dichroicmirror 58, are incident upon the incident side polarizing plate 64.Thereafter they are output from the incident side polarizing plate 64and are then incident upon the first color selective phase differenceplate 65 which has a function of rotating the polarizing direction ofthe B-light alone by an angle of 90 deg., and accordingly, the B-lightwhich is P-polarized and the R-light which is S-polarized are incidentupon the second polarized beam splitter 66. Thus, the R-light which hasbeen incident upon the second polarized beam splitter 66, beingS-polarized, is reflected by the polarization separation surface of thesecond polarized beam splitter 66, and comes to the R-light reflectiontype liquid crystal display element 61R. Further, the B-light which hasbeen incident upon the second polarized beam splitter 66, beingP-polarized, is transmitted through the polarization separation surfaceof the second polarized beam splitter 66, and comes to the B-lightreflection type liquid crystal display element 61B. Since the R-lightreflection type liquid crystal display element 61R exhibits black, theR-light incident upon the R-light liquid crystal display element 61R isreflected without being image-modulated. Accordingly, even after thereflection by the R-light reflection type liquid display element 61R,the R-light is still S-polarized as it is, and accordingly, it isreflected at the polarization separation surface of the first polarizedbeam splitter 60, being then transmitted through the incident sidepolarizing plate 64 and returned to the light source side, and isremoved from the projection light. Thus, black is displayed. Meanwhile,the B-light incident upon the B-light reflection type liquid crystalelement 61B is reflected without being image-modulated since the B-lightreflection type liquid crystal display element 6 exhibits black. Thus,since the B-light is still P-polarized as it is even after it isreflected by the B-light reflection type liquid crystal display element61B, it is transmitted again through the polarization separation surfaceof the first polarized beam splitter 60, and is changed by the firstcolor selective phase difference plate 65 into S-polarized light whichis then transmitted through the incident side polarizing plate 64 so asto be returned to the light source surface, and is removed from theprojection light.

Thus, the projection type image display apparatus using the reflectiontype liquid crystal display elements (reflection type liquid crystalpanels) has the optical configuration as stated above.

In this third embodiment, although the color separation and synthesissystem 200 is incorporated therein with the wavelength selective phasedifference plate and the like, if the polarized beam splitter arrangedin the color separation and synthesis system 200 has a polarizationseparation film which serves as a polarized beam splitter in a specifiedwavelength range within the visible range but which transmits orreflects light therethrough or thereupon in the other wavelength range,irrespective of the direction of polarization, it may be considered thatthe wavelength selective phase difference plate is not required.Further, a ¼ phase difference plate can be arranged between the colorseparation synthesis system 200 and the projection lens 70 in order toprevent light which is reflected at and returned from a lens surface inthe projection lens 70, from being reflected back in the directiontoward the screen (the direction toward the surface to be illuminated).

Further, in the third embodiment, although the explanation has been madeof the presence of three liquid crystal display elements, the number ofliquid crystal elements is not limited to three but can be 2 or 4. Itcan be, of course, 1.

As stated above, according to this embodiment, there can be provided anillumination optical system which has a high light available efficiencyand which can illuminate the surface to be illuminated, substantiallyuniformly thereover, and also an image display apparatus using theillumination optical system.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

What is claimed is:
 1. An illumination optical system for illuminating asurface to be illuminated comprising: a lens array system configured tosplit a light beam from a light source in a first plane which isparallel to an optical axis of the illumination optical system, aplurality of first light source images are formed in a first lightsource image zone with the use of the thus split light beams, and lightbeams from the plurality of first light source images are led to thesurface to be illuminated, the lens array system further configured tosplit the light beam from the light source in a second plane which isparallel to the optical axis of the illumination optical system andwhich is perpendicular to the first plane, a plurality of second lightsource images are formed in a second light source image zone with theuse of the thus split light beams, and light beams from the plurality ofsecond light source images are led to the surface to be illuminated, anda polarization separation surface which is arranged at an inclination tothe optical axis of the illumination optical system, wherein the widthof the first light source image zone in the first plane is larger thanthat of the second light source image zone in the second plane, andwherein the second plane is parallel with a normal line to thepolarization separation surface and the optical axis of the illuminationoptical system.
 2. An illumination optical system according to claim 1,wherein the lens array system includes a second lens array having asecond front side optical element array, including a plurality ofoptical elements, for splitting the light beam from the light source inthe second plane, a second rear side optical element array, including aplurality of optical elements corresponding to the plurality of opticalelements in the second front side optical element array, for receivinglight from the second front side optical element array, and acompressing device located between the light source and the second rearside optical element array for compressing the width of the light beamfrom the light source in the second plane.
 3. An illumination opticalsystem according to claim 1, wherein the lens array system includes afirst lens array having a first front side optical element arrayincluding a plurality of optical elements, for splitting the light beamfrom the light source in the first plane, a first rear side opticalelement array including a plurality of optical elements corresponding tothe plurality of optical elements in the first front side opticalelement array, for receiving light from the first front side opticalelement array, and wherein the lens array system further includes asecond lens array having a second front side optical element arrayincluding a plurality of optical elements, for splitting the light beamfrom the light source in the second plane, and a second rear sideoptical element array including a plurality of optical elementscorresponding to the plurality of optical elements in the second frontside optical element array, for receiving light from the second frontside optical element array, and wherein the first rear side opticalelement array and the second rear side optical element array are locatedat positions which are different from each other.
 4. An illuminationoptical system according to claim 3, wherein the first rear side opticalelement array is located nearer to the light source than the second rearside optical element array.
 5. An illumination optical system accordingto claim 1, wherein the optical beam for illuminating the surface to beilluminated has an angular distribution in the first plane which isdifferent from the angular distribution, of the light beam forilluminating the surface to be illuminated, in the second plane.
 6. Anillumination optical system according to claim 1, wherein an opticalbeam incident upon the surface to be illuminated has a diverging anglewhich is larger than the diverging angle, of the light beam incidentupon the surface to be illuminated, in the second plane.
 7. Anillumination optical system according to claim 1, wherein the lens arraysystem includes: in order from the light source side a first front sidecylindrical lens array including a plurality of cylindrical lenseshaving refractive powers in the first plane, a first rear sidecylindrical lens array including a plurality of cylindrical lenseshaving refractive powers in the first plane, a second front sidecylindrical lens array including a plurality of cylindrical lenseshaving refractive powers in the second plane, and a second rear sidecylindrical lens array including a plurality of cylindrical lenseshaving refractive power in the second plane.
 8. An illumination opticalsystem according to claim 7, wherein the incident light beam which isincident upon the first rear side cylindrical lens array has a lightbeam width in the direction of the first plane, which is larger than thelight beam width, in the direction of the second plane, of the incidentlight beam which is incident upon the second rear side cylindrical lensarray.
 9. An illumination optical system comprising: a first opticalelement array including a plurality of optical elements havingrefractive powers in a first plane containing the optical axis, forsplitting light from an optical source into a plurality of partial lightbeams, a second optical element array including a plurality of opticalelements having refractive powers in a second plane, for transmittingthe plurality of partial light beams onto a surface to be illuminated, asuperposing optical element for superposing the plurality of partiallight beams output from the second optical element array with oneanother on the surface to be illuminated, a compressing device forcompressing the width, in the first plane, of the light beam from thelight source, and a polarization separation surface which is arranged atan inclination to the optical axis of the illumination optical system,wherein the refractive powers of the compressing device in the secondplane is larger than that in the first plane which contains the opticalaxis, the second plane perpendicular to the first plane, and wherein thesecond plane is parallel with a normal line to the polarizationseparation surface and the optical axis of the illumination opticalsystem.
 10. An image display apparatus comprising: at least one liquidcrystal display element, and an illumination optical system according toclaim 1, for illuminating the at least one liquid crystal displayelement with light from the optical source.
 11. An image displayapparatus comprising: at least one liquid crystal display element, andan illumination optical system according to claim 9, for illuminatingsaid at least one liquid crystal display element with light from thelight source.